Locking mechanism for doors



Feb. 13, 1934.

D. F. SMITH ETAL LOCKING MECHANISM FOR DOORS Filed May 9, 1 93s $3M WMXM NVENTORS WQMMZ JZLM/ ATTORNEY Patented Feb. 13, 1934 LOCKING MECHANISM FOR DOORS Daniel F. Smith, New York, N. Y., and William F. Purcell, Hoboken, N. J.

Application May 9,'1933. Serial No. 670,058

5 Claims.

This invention relates to locking mechanisms for doors, and particularly to mechanisms which permit the occupant of a house or apartment to see who seeks admission before opening the door.

It is common practice to provide a door with a safety chain which, when attached, prevents the full opening of the door. This device, however, does not fully meet the requirements, as the occupant is very likely to forget to attach the chain. The object of this invention is to provide a simple and eiiective device which the occupant cannot forget to use.

The invention consists in providinga locking mechanism which cannot be unlocked, from within, until a safety chain, or equivalent thereof, has been attached and in certain details of construction and arrangement of parts as illustrated, described and claimed herein.

In the accompanying drawing:-

Fig. 1 is an elevation of a lock of the well known night latch type, showing an embodiment of our invention therein.

Fig. 2 is an end view of the latch-plate.

Fig. 3 is an end view of the lock.

Fig. 4 is a bottom view of the lock.

Fig. 5 is a sectional view, taken on the line 5-5 of Fig. 1, of the chain terminal and Fig. 6 is an elevation of the back of the lock with the cover plate removed.

Referring to the drawing by reference numerals, 1 indicates the lock casing, 2 the latch-plate and 3 the latch-bolt. The latter is of usual construction, having a cross plate 3' at one end and a beveled head 3" at the other. A lug 4 is provided on the casing which lug is slotted to guide the latchbolt and also serves to secure the back plate 5 by means of a screw at 6. A compression spring 7 is placed between the lug 4 and the head 3" of the latch-bolt, which urges the bolt outwardly and causes the bolt head to snap into and engage the latch-plate 2 when the door is closed. The numeral 8 indicates a knob having a stem 9, which projects through a hole in the casing and a disk 10 is riveted or otherwise secured to this stem, so that when the knob is rotated the disk will also be rotated. Projecting from this disk are two studs 11 and 11' which engage the cross plate 3' and limit the outward movement of the latchbolt 3 when'both studs are. in contact with the plate, as shown in Fig. 6, and it will be apparent that if the disk 10 be rotated, either in a clockwise or counter clockwise direction, one of said studs will engage the plate 3' and withdraw the latchbolt 3, against the tension of the spring 7, from engagement with the latch-plate 2, the cross plate 3' moving back until it strikes the stops 12.

A second disk 13 carrying studs 14 and 14' is secured to a member 15, which is rotatably mounted on the back plate 5 of the lock. This member is adapted-to be rotated by means of a key from the outside of the door and the function of the disk, when so rotated, is the same as that of the one before described. It will be noted.

'that these two disks are independent of each other and that the latch-bolt 3 can be withdrawn, by means of a key, fromthe outside of the door without turning the knob 8.

The disk 10 is provided with a notch 16 adapted to receive one end of a pawl 1'7, which is pivotally mounted on the inside of the lock casing at 18, a whip spring 19 bears against one end of this pawl and urges the other end upward to engage the notch 16 in the disk 10 and it will be seen that when the notch is so engaged, as shown in Fig. 1, the knob 8 cannot be rotated and therefore the latch-bolt cannot be withdrawn and the door cannot be opened from the inside.

The numeral 20 indicates a chain one end of which is preferably attached to the latch-plate 2. This chain is provided at its free end with a terminal adapted to be inserted in a T shaped opening 21 in the lock casing and moved, in the direction indicated by arrows, to the end of the slot 21' as shown in Fig. 6. This action by the operator will attach the safety chain to the lock and will change the position of the pawl 17, from that shown in Fig. 1 to that shown in Fig. 6, thereby releasing the pawl from engagement with the disk 10 and permitting the knob 8 to be rotated to unlock the door.

From the fore-going description, it will be seen that a door equipped with this device cannot be unlocked from within until the safety chain has been attached thereto, thereby permitting a partial opening of the door, for observation, but preventing the entrance of a person on the outside unless the person within detaches the chain.

Modifications of the invention may be made to adapt it to different types of locks. With some types of looks it may be desirable to cause the attachment of the chain to move a latch and unlock the door directly. Well known means. for accomplishing this will occur to those skilled in the art and further explanation is thought to be unnecessary.

We do not limit ourselves to the precise construction shown; but claim as our invention:-

1. In a locking mechanism for a door, the combination with a. lock of a safety chain, one end of said chain being permanently attached to the door frame and one end adapted to be attached to the lock, and means for preventing said lock being unlocked from one side of the door until the chain is attached to the lock.

2. In a locking mechanism for a door, the combination with a lock having a latch-bolt of a pawl to prevent withdrawal of said latch-bolt, when the door is looked, a safety chain adapted to be attached to said lock and means for causing the attachment of said chain to move said pawl so as to permit the withdrawal of said latch-bolt.

3. In a locking mechanism for a door, the combination with a lock having a latch-bolt and a rotatable member for withdrawing said latch bolt, of a pawl adapted to prevent rotation of said member, when the door is looked, a safety chain adapted to be attached to said lock and means for causing the attachment of said chain to the lock to permit rotation of said rotatable member.

4. In a locking mechanism for a door, the combination with a lock of a member, detachabletherefrom, and adapted, when attached, to prevent full opening of the door and means for 

